Damian Kowal

Comparison of Iron Loss Models for Electrical Machines With Different Frequency Domain and Time Domain Methods for Excess Loss Prediction

The goal of this paper is to investigate the accuracy of modeling the excess loss in electrical steels using a time domain model with Bertottis loss model parameters n0 and V0 fitted in the frequency domain. Three variants of iron loss models based on Bertottis theory are compared for the prediction of iron losses under sinusoidal and non-sinusoidal flux conditions. The non-sinusoidal waveforms are based on the realistic time variation of the magnetic induction in the stator core of an electrical machine, obtained from a finite element-based machine model.

Comparison of Nonoriented and Grain-Oriented Material in an Axial Flux Permanent-Magnet Machine

The performance and iron losses of an axial flux permanent-magnet synchronous machine (AFPMSM) using nonoriented (NO) steel are compared with the performance and iron losses of an AFPMSM using grain-oriented (GO) material. The machine is modeled by several 2-D finite element models in circumferential direction, at different radii. The material model for the GO material is an anhysteretic anisotropic model based on the magnetic energy. The magnetic energy is computed by using several measured quasi-static BH-loops on an Epstein frame in seven directions starting from the rolling direction to the transverse direction. The losses are calculated a posteriori, based on the principles of loss separation and dynamic loop measurements. A loss model was made for each of the seven directions, assuming unidirectional fields. In comparison with the more usual NO material, both the saturation induction and the torque are higher with GO material. The magnetic field in the GO material is lower than for NO material in the major part of the iron, but higher in the tooth tips where the field is not in the rolling direction. The stator iron losses are about 7 times lower for the considered GO compared to the NO material.

Influence of the Electrical Steel Grade on the Performance of the Direct-Drive and Single Stage Gearbox Permanent-Magnet Machine for Wind Energy Generation, Based on an Analytical Model

The performance of a variable speed wind turbine using a direct-drive permanent-magnet synchronous generator (PMSG) as well as a PMSG with single stage planetary gearbox is compared for two grades of electric steel applied for the generator stator core lamination. A ring type, radial flux PMSG is modeled. For a fixed mechanical power input, the geometry of the generator is optimized for each turbine systems and two materials to maximize the annual efficiency of the generator. The annual efficiency is calculated based on the power curve of the generator and the probability density function of the wind speed. This function is approximated by the Weibull distribution function for a site with average wind speed of 7 m/s. For both generator systems, the annual efficiency of two optimized generators using different steel grades differs around 1%. The difference depends on a mass of active material of the generator.

Comparison of Frequency and Time-Domain Iron and Magnet Loss Modeling Including PWM Harmonics in a PMSG for a Wind Energy Application

This paper presents the calculation of the electromagnetic losses for a 2.1-MW permanent magnet synchronous generator for wind energy application. The focus is on recognizing the significance of including the analysis of higher harmonics in the electromagnetic loss calculation. The analyzed harmonics include the ones resulting from the use of a pulse width modulation (PWM) of the voltage of the generator. The magnet losses calculated for the PWM current are several times higher than the ones calculated for the sinusoidal current. In addition, frequency-domain and time-domain models for iron loss calculation are compared. The frequency-domain model that assumes a sinusoidal variation and considers only the fundamental component of the magnetic induction in the stator core material underestimates the iron losses in the machine. Especially, when the additional losses resulting from the higher harmonics, rotational fields, and minor loops are taken into account. Finally, it is shown how the composition and thickness of the electrical steel used in the stator core of the generator influences the total core losses.

The Effect of the Electrical Steel Properties on the Temperature Distribution in Direct-Drive PM Synchronous Generators for 5 MW Wind Turbines

The effect of the magnetic and thermal properties of four electrical steel grades were compared for a permanent magnet synchronous generator (PMSG). The low loss grades are expected to have less iron loss in the stator laminations, but their thermal conductivity may be lower. Therefore, the evacuation of the heat may be less effective. This has an influence on the temperature distribution, which is crucial in case of PMSG. The investigated generator is a 5 MW, radial flux machine designed for direct-drive wind turbines. A thermal finite-element model was used to simulate the temperature distribution in the generator. The influence of the steel grade on the thermal distribution was compared for four geometries of PMSG with varying air-gap diameter and pole-pair number. In conclusion, the number of pole pairs has a major influence on the importance of electrical and thermal properties of the steel grades applied.

Influence of the electrical steel grade on the performance of the direct-drive permanent magnet machine for wind energy generation

The performance of a variable speed, direct-drive synchronous generator wind turbine concept is compared for two grades of electric steel applied for the generator stator core lamination. A ring type, radial flux permanent magnet synchronous generator (PMSG) is modelled. For a fixed mechanical power input, the geometry of the PMSG is optimized for each material to maximize the annual energy yield. The energy yield is calculated based on the power curve of the generator and the probability density function of the wind speed. This function is approximated by the Weibull distribution for a site with average wind speed of 7 m/s. The annual efficiency differs more than 2% between the two optimized generators, which use different grades of material.